nvmeof-mp/rc: fix nvmeof-mp failure when NVME_TARGET_PASSTHRU enabled

nvmeof-mp/rc: fix nvmeof-mp failure when NVME_TARGET_PASSTHRU enabled

$ ./check nvmeof-mp/001
nvmeof-mp/001 (Log in and log out)                           [passed]
    runtime  0.400s  ...  0.457s
rmdir: failed to remove 'subsystems/nvme-test/passthru/admin_timeout': Not a directory
rmdir: failed to remove 'subsystems/nvme-test/passthru/device_path': Not a directory
rmdir: failed to remove 'subsystems/nvme-test/passthru/enable': Not a directory
rmdir: failed to remove 'subsystems/nvme-test/passthru/io_timeout': Not a directory

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Yi Zhang <yi.zhang@redhat.com>